1. Field of the Invention
The present invention relates to an accuracy analyzing apparatus for a machine tool having a feed mechanism for relatively moving a table and a spindle along orthogonal three axes including a first axis extending along a spindle axis and second and third axes perpendicular to each other and perpendicular to the first axis, the accuracy analyzing apparatus being adapted to analyze the perpendicularity of a spindle axis with respect to the second axis and/or the third axis and the thermal displacement of the spindle.
2. Description of the Prior Art
The perpendicularity of a spindle axis directly affects the machining accuracy and, therefore, is usually checked and adjusted to satisfy a predetermined reference value before being shipped from a machine tool maker to a user.
A conventional method for checking the perpendicularity is as follows. A straightedge is attached to a table to be fed by a feed mechanism, and a dial indicator is attached to a spindle. While the spindle is moved along a first axis with one of two measuring surfaces of the straightedge positioned along a second or third axis, measurements are taken on the other measuring surface of the straightedge by means of the dial indicator.
When the spindle is rotated, bearings rotatably holding the spindle generate heat due to rolling of rolling elements thereof, so that the spindle is liable to be displaced (or extended) along the spindle axis by the generated heat thereby to cause a machining error. For correction for the thermal displacement, it is a conventional practice to measure a temperature around the spindle and estimate the thermal displacement (extension) amount along the spindle axis on the basis of the measured temperature.
However, the analysis of the perpendicularity of the spindle axis and the estimation of the thermal displacement amount of the spindle cannot be achieved by a single apparatus as can be understood from the above description. Therefore, separate apparatuses should be provided for the analysis and the estimation. This leads to lower efficiency and higher costs.
Since the thermal displacement of the spindle is estimated on the basis of the temperature measured around the spindle but not the temperature of the spindle itself, the estimation of the thermal displacement amount is not always accurate.
In view of the foregoing, it is an object of the present invention to provide an accuracy analyzing apparatus which is capable of highly efficiently analyzing the accuracies of a machine tool including the perpendicularity of a spindle axis and the thermal displacement of a spindle with a higher level of accuracy at lower costs.